1. Field of the Invention
The present invention relates, in general, to internally or externally threaded fasteners or nuts or bolts used for fastening or joining two or more separate parts of an article or structure and, more particularly, to a secure threaded fastener provided with a coil spring capable of preventing the fastener from unexpectedly coming loose.
2. Description of the Prior Art
Internally or externally threaded fasteners: nuts or bolts are well-known fasteners, which have been widely used for joining two or more separate parts of an article or structure. Therefore, the soul of such threaded fasteners is their tightness, which joins separate parts without allowing the fasteners to be unexpectedly loosened.
However, typical threaded fasteners may lose their tightness due to vibrations, impacts or temperature change, thus being unexpectedly loosened and failing to securely join separated parts.
In an effort to prevent such an unexpected looseness of threaded fasteners, several types of devices for improving the tightness of the fasteners are proposed and widely used.
Washers, fluted nuts, split pins and snap rings are examples of such tightness improving devices. Typical washers used are spring washers, plane washers and washer based nuts. A typical fluted nut is used with a split pin and is provided with a diametrical groove or hole for the split pin at the top portion. Meanwhile, a typical snap ring is elastically fitted over the shank of a bolt at a position around a nut tightened to the bolt, thus stopping the nut and preventing the nut from being unexpectedly loosened.
However, such typical tightness improving devices are problematic in that they fail to effectively improve the tightness of threaded fasteners as will be described hereinbelow.
That is, typical washers are designed to reduce impact vibrations applied to threaded fasteners. Therefore, such washers fail to completely prevent unexpected looseness of the fasteners and only prevent a rapid looseness.
On the other hand, the fluted nuts with split pins are designed to be prevented from being removed from bolts. However, such fluted nuts are not designed to basically prevent looseness of nuts, thus failing to keep the tightness of nuts or bolts.
In order to overcome the problems experienced in typical washers or washer based nuts, a toothed washer based nut is proposed. Such a toothed washer based nut has a somewhat improved tightness due to a toothed surface of the washer. However, such an improvement in the tightness provided by the toothed washer is not enough to keep the desired tightness of threaded fasteners, thus failing to completely prevent the fasteners from being unexpectedly loosened.
As described above, the soul of threaded fasteners is their tightness resisting against unexpected looseness. Particularly, when threaded fasteners, used for joining separated parts of normally vibrated articles or structures such as machinery, automobiles or airplanes, do not effectively keep their tightness, the separated parts joined by the fasteners may be unexpectedly loosened and moved relative to each other. In such a case, the loosened and moved parts may cause an operational error and fail to perform their desired function, resulting in a breakdown or safety hazard.